Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$75.45	5.145%	$79.3319	$79.33	$79.35	$79.30
Purchase #2	$235.91	13.703%	$268.2367	$268.24	$268.25	$268.20
Purchase #3	$27.41	11.405%	$30.5361	$30.54	$30.55	$30.50
Purchase #4	$82.58	5.676%	$87.2672	$87.27	$87.25	$87.30
Purchase #5	$232.56	12.452%	$261.5184	$261.52	$261.50	$261.50
Purchase #6	$196.39	6.388%	$208.9354	$208.94	$208.95	$208.90
Purchase #7	$158.64	3.835%	$164.7238	$164.72	$164.70	$164.70
7 purchase totals =	$1,008.94		$1,100.5495	$1,100.56	$1,100.55	$1,100.40